Power-line signaling



July 24, 1928. 1,678,133

I. w. v. WOLFE POWER LINE 5 IGNALIN G Filed Sept. 22, 1925 2 Sheets-Sheet 1 W M j July 24, 1928.

W. V. WOLFE POWER LINE SIGNALING Filqd szepo. 22, 1925 2 Sheets-Sheet 2 Patented July 24, 1928.

lTED STATES PATENT OFFICE. s

WALLACE V. WOLFE, OF GLEN RIDGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

POWER-LINE SIGNALING.

Application filed September 22, 1923. Serial No. 664,147.

waves upon the power currents traversing the power line.

An object of the invention is to provide for full duplex telephone communication over power lines.

lit

Another object is to provide for selective ringing in connection with telephone systems on power lines whereby any station may call any other station without ringing other stations or whereby any station may call the other stations if desired.

Another object is to provide for connecting signaling apparatus to a power line for transn'iission thereover by such coupling apparatus as will combine ellicient signaling with safety to persons communicating by means of signaling apparatus and with safety to the apparatus itself. Other objects are to provide for telephone and signaling operation over high power transmission lines in which the transmitting volume will be sufiicient for transmission under both normal and abnormal conditions over either long or short lines, in which a full metallic high frequency circuit. is employed in order to avoid the numerous difficulties connected with ground return circults, and furthermore, to employ for communication such carrier frequencies as will not interfere with existing communication systems and particularly with carrier wave telephone systems parallel with the power lines. An ancillary object is to avoid any interference of harmonics of the power line current, static or other impulsive disturbances, and other communication systems, with the power line signaling system.

Special objects are to provide simple and automatically operating amplification control of a device whereby it may operate as an ellicient detector for telephone communication and as an efiicient rectifier for calling operation.

An important object is to provide for safely and efiiciently coupling high frequency signaling apparatus to high voltage transmission lines.

In a particular embodiment any desired number of stations, twoor more, are coupled to two conductors of a three-phase transmission line operating at voltages of the order of 110,000 volts. The equipment at each station comprises an operators or subseribers telephone apparatus connected to outgoing and incoming carrier channels. In the outgoing channel are generating and modulating apparatus and amplifying apparatus to increase the modulated oscillations to any power desirable or necessary for transmission. The incoming channel is provided with a filter adapted to exclude waves of the frequency being transmitted thus enabling duplex communication. The station originating the call always transmits upon one of two selected frequencies and the station receiving the call always operates upon the other select carrier frequency. Relays are providedfor interchanging the normal position of the incoming and outgoing channel filters at the call originating station before communication begins. In the normal position, each station is in call re ceiving condition. The receiving channel at each station comprises a suitable amplifier of the proper number of stages and a device which serves as a rectifier for calling purposes. The polarized battery of the rectifier is automatically changed during talking in order to increase its efliciency as a speech detector. Station selection is accomplished by means of selective apparatus consisting of the well'known type of selector, hereinafter described, which is combined with the high frequency circuit in a manner to be properly actuated by incoming waves.

The invention will be best understood both as to the details of its organization and its mode of operation by reference tothe following description taken in connection with the accompanying drawing, in which is shown in Fig. l a circuit diagram of the essential features of the apparatus employed at one station; in Fig. 2 an aerial arrangement for coupling the signaling circuit to the power line in a safe and efiicicnt manner which may be substituted for that portion of the circuit of Fig. l to the right of the line XX, and Figs. 3, 4, 5 and 6 show modified forms of coupling circuits which may be substituted for the coupling circuit of Fig. 1 between the dotted lines YY and XX when the modified form or any equivalent arrangement of Fig. 2 is employed. Fig. 1 is a circuit diagram of the apparatus whereby an operator at the station 1 or a subscriber at a subscribers stat-ion 2 may communicate over a high voltage transmission line '3 with other subscribers or operators located at distant points on the transmission line. At each distant station terminal apparatus similar in arrangement and function to that illustrated in the drawing will be provided. By high voltage trans mission line? is to be understood any system or network of conductors for the electrical transmission of power over which it is possible to transmit high frequency waves.

The terminal apparatus illustrated iii the drawing comprises, (1) an outgoing channel, and (2) an incoming channel. The opcrators telephone set 1 is arranged to be connected to these channels simultaneously by means of a switch or key 4. In the left-hand position of the switch 4, the signaling channel may be extended by means of a hybrid coil 5 to a cord and plug connection 6 at a telephone switchboard whereby the circuit may be further extended to any subscriber or telephone network.

The outgoing channel comprises (1) a high frequency wave generator 7 designed to produce waves at two different high frequencies, for example, 80,000 and 100,000 cycles persecond, which will hereinafter be referred to as frequencies f, and 7, respectively; (2) an amplifying and modulating tube 8 and its associated circuits whereby the outgoing waves are modulated in accordance with speech; (3) an amplifier 9 and its associated circuits whereby the waves produced by the oscillator 7 may be amplified. to sufficiently high power for transmission under normal conditions; 1) an auxiliary amplifier 10 and its associated circuit connections which may be connected into circuit to increase the power amplification for transmission under abnormal conditions, as for example. when a section of the line is down; (5) high pass and low pass filters 11 and 12 which may be included in the transmission circuit alternatively by means of apparatus hereinafter described; (6) a coupling circuit 13; and (7) coupling capacities 14, the coupling circuit and coupling capacities being common to the incoming and outgoing transmission channels and serving to couple the signaling apparatus with a selected pair of power line conductors.

The receiving channel extends from the power line through the coupling condensers 1 1, the coupling circuit 13, to the high pass or low pass filter 11 or 12, and includes, in additioirtothese elements,- 1) high frequency amplifying apparatus 15 for amplifying in one or more stages the incoming waves, and (2) a rectifying or detecting tube 1(. For calling purposes, the incoming channel is normally extended by means of relays through the circuit of a selector 17, which controls a bell or other signaling device 18. The selector 17 is the type of device described and claimed in the patents to J. C. Field. No. 1,200,095, granted October 6, 1916 and No. 1,343,256, granted June 15, 1920.

For efficient signaling it is essential that the signaling circuit be connected with the power line in such a manner as to effect a tween the terminals of the signaling circuit a and the conductors of the power line. Such a capacity may be provided by a fixed condense-r adapted to withstand the high voltages or an arrangement of aerial wires arranged adjacent to the power line conductors. It has been proposed to employ a section of high voltage cable, the cord of which constitutes the power line conductor and the sheath of which. serves as a plate of a condenser to which the signaling circuit is connected. However, the manufacture of cable adapted to continuously withstand the high voltages met with isa matter of considerable difiiculty. The preferred coupling ar-.

rangement consists of a fixed condenser with either oil or porcelain dielectric or an antenna arrangement. The coupling circuit comprises condensers 19 and choke coils 20 in series with the line and condensers 21 and choke coils 22- in shunt to the line. coils 22 serve also to shunt to ground any 60 cycle current entering the coupling circuit. Choke coils 23 are connected in the line adjacent the coupling condensers 14. Safety devices comprise fuses 2-4:, openair spark gaps 25 and 26 of high current capacity and vacuum gaps 27 in shunt. to the gaps 26.

The

The vacuum gaps break down quickly under the influence of excessive voltages, and thus serve to protect the signaling circuit until the air gaps 26, which are adapted to carry a much heavier current than the vacuum gaps, come into operation.

Operation in caZZing.-The switch 4; is closed at its right-hand contacts thus connecting the operators set 1 to the high frequency circuit, closing the contact 30 and opening the contact 31. When the-operator takes his receiver from the switchhook, the contact 32 is closed, thereby connecting ground to the conductor 33. The relays 34, 35 and 36 then operate. Since the selector keys SK. SK are normally closed, the operation of the relay 34 closes the contact on the inner armature and thus operates the relay 37. It will first be assumed that line conditions are normal and that the auxiliary amplifier is not to be used, in which case the relay 35, although closed, performs no function. Under such conditions, the switch 51 is closed in the down position. The relay 36 closes the filament heating circuits of the modulating, generating and amplifying apparatus 8, 7, 9. The operator now actuates one of the keys Slfcorresponding to the station desired to be called and thus causes the relay 37 to operate each time a tooth of the selector key opens the circuit of the relay 37 thereby placing the condenser 38 into and out of circuit once for each impulse transmitted by the. selector keys. The condenser 39 which is permanently connected in circuit determines the high carrier frequency f,, and the addition of condenser 38 in parallel determines the low carrier frequency f,. Normally, the high pass filter 11 is connected to the transmitting channel and the low pass filter 12 is connected to the receiving channel; However, when the relay 34 was operated as aforesaid, the relays and 41 became operated and thus interchanged the high pass and low pass filters'so that the low pass filter 12 is connected to the transmitting circuit and the high pass filter 11 is connected to the receiving circuit. During the operation of the selector key, the frequency generated by the oscillator 7 is thus changed back and forth from the low carrier frequency to the high carrier frequency f and vice versa. However, the high carrier frequency is not transmitted to the line in asmuch as the low pass filter is designed to pass only the low carrier frequency and to suppress the high carrier frequency. The groups of impulses of the low carrier frequency are thus transmitted to and impressed upon the power line, When the selected station answers, the operator at the calling station may converse by means of his telephone set and if desired he may extend the connection through the hybrid coil 5 and the plug 6 to a telephone switchboard or any subscriber whose line is permanently attached to the plug connection 6. When throwingthe switch '4 from the right-hand transmit-s on the lower of the two frequencies and receives on the higher.

position to the left-hand position it is essentxal that the contact 31 be made before the .contact 30 is broken in order to hold the ground upon the conductor 33 and thus maintain the circuit,

When the oscillator 7 at the called station transmits high frequency impulses to the line, relays 42 and 43 at the calling station are not actuated because the relay 34 has prepared short circuit around the relay 42. The station originating a call always carrier If desired the higher frequency may be used for calling and the lower for answering.

Operation at (1 called station-The electrode circuits of the amplifier 15 and the rectifier-detector 16 are normally energized. Incoming high frequency impulses are rectilied by the rectifier 16. This increases the space current of the rectifier 1G and operates the marginal relay 42 inasmuch as the middle armature contact of the relay 34 is opened. The operation of the relay 42 causes the operation of the relay 43, thus closing its left-hand contact and connect ng the battery through the relay 44 which causes it to operate and supply an impulse of current to the electromagnet of the selector 17 which causes the selector to operate one step. When the incoming oscillatlons cease, the relays 42, 43 and 44 release Which.

causes an impulse of current of opposite sign through the magnet of the selector 1?. A proper series of impulses will cause the selector to close the circuit of the bell 18. At the cessation of the calling impulses, the frequency is continuously transmitted to the line at the calling station and the relays 42 and 43 are maintained operated at the called station. Therefore, when the 0peratorat the called station removes his receiver from the switchhook and places ground upon the conductor 33, thus operating the relay 34, the relays 40,41 and 37 do not operate because the. path to ground through the inner contact of the relay 43 is broken. Consequently, the high pass filter 11 at the called station remains connected to the transmitting channel and the low pass filter 12 remains connected to the receiving channel. The generator 7 oscillates at the higher .carrier frequency f, and sends to the line a continuous train of oscillations through the high pass filter 11. The operators or subscribers may now converse with each other inasmuch as at each station the outgoing oscillations will be modulated in accordance with speech and the incoming oscillations will be detected by the detector 16 and impressed upon the telephone circuit. The called station always transmits on the higher of the two carrier frequencies and receives on the lower. quencies may be reverse of that stated if desired.

Operation at an idle statz'0n.-When oscillations of the frequency f, are impressed upon the line, the relays 42, 43 and 44 are actuated once for each group of impulses.

However, if the spacing of the impulses is not that for which the selector 17 is set, the selector 17 does not close the circuit of the bell 18, but, at the cessation of the incoming Of course the use of frelO-d impulses, the selector returns to its normal position. Each impulse of current of the frequency 1 will actuate the relays 42 and 43 as stated efore and the left-hand contact of the relay 43 closes a circuit through the lamp 45. \Vhen the called station answers and high frequency current is continuously upon the line, the relay 43 is maintained .in a manner which will be obvious.

energized and the lamp 45 remains lighted, thus indicating that the circuit is busy. Operators at idle stations are thus warned not to attempt to call upon the circuit wherby they are able to avoid interfering with conversations in progress.

Emergency key opcmii0n.lf line conditions are too abnormal to allow code selective ringing, if the selector circuits are not operating properly, if there are only two stations upon the line, or, if it is desired to arrange so that all the stations may be called simultaneously from a chief operators or dispatchers station, the key 46 may be operated. High frequency impulses put upon the line will then cause the relay 43 to close a circuit directly through the bell 18. If continuous oscillations are put upon the line, the bell 18 at each station where key 46 is operated will ring continuously or any predetermined code of ringing may be employed. The selector keys SK in this case are employed to transmit impulses or a hand key may be used in place of the selector keys It is customary in connection with the use of selectors such as the selector 17 to provide one selector key SK at a chief dispatchers office with an arrangement of teeth adapted to call all the stations upon the line simultaneously. This mode of operation may be employed in the present instance, if, for example, an emergency renders it-necessary for the dispatcher to give directions to attendants at all the stations simultaneously. Automatic gain control operation-+14 marginal relay 60 serves to control the amplification of the amplifier 15. With signaling waves of normal amplitude coming into the receiving circuit, the relay 60 remains unoperated. Waves of amplitude above normal cause such an increase in the space current of the tube 16 as to operate the relay 60 thus placing in the circuit an artificial line 61 which cuts down the amplitude of the waves impressed upon the input circuit of the amplifier 15. The circuit is preferably adjusted so that the relay 60 will not again release unless the amplitude of the incoming waves falls below that necessary to cause it to operate. The relay 60 and the artificial line 61 may be omitted in case their use is unnecessary and other means may be used to control the signaling volume in case such control is necessary. A condenser 59 serves to shunt high or carrier frequency waves around the relay 42.

Rectifier-detector control operation-Jinder normal conditions, the tube 16 has applied to its grid the full negative potential of the source 62 so that it operates very efficiently as a rectifier for rectifying the groups of waves put upon the line for calling purposes. When the operator at the receiving station answers a call and places a ground upon a conductor 33, the relay 34 is operated in the manner hereinbefore specified and-the contact on its outer right-hand armature is broken and the inner contact closed. This places a reduced negative potential upon the grid of the tube 16 whereby it is conditioned for maximum efiiciency for the detection of voice modulated carrier waves. lVhen the conversation is finished the relay 34 releases and the tube 16 is again conditioned for rectification of calling waves. At the calling station the same operation takes place upon moving the telephone receiver from the switchhook and the tube 16 is conditioned for detection of telephone waves during periods of conversation.

Auxiliary amplifier circuit 0pemti0n.1f line conditions are bad owing to a break in the line or a section of the line being down, the switch 51 is moved from the normal down position to the up position, thus connecting a power source 52 to the motor generator 53 and energizing the plate and filament circuits of the power amplifier 10. The outgoing channel will then extend from the plate circuit of the amplifier 9through the high frequency transformer 54 to the grid circuit of the amplifier 10 and from the plate circuit of the amplifier 10 through the high frequency transformer 55 and the high or low pass filter 11 or 12, as the case may be, to the line. The tube 10 is an amplifier of considerable output, capable of supplying from five to twenty times more energy than the power normally used for transmitting.

It is contemplated that the coupling circuit 13 should have the transmission characteristic of a very flatly tuned circuit or preferably that it should have the characteristic of a band pass filter, thus transmitting with negligible attenuation currents of frcguencies of 80,000 and 100,000 cycles per second or whatever frequencies are used in the particular system. A band pass filter passes a band of frequencies with substantially uniform and small attenuation and greatly discriminates against currents of'other frequencies. Such a band filter characteristic may be obtained by properly choosing the capacities 19 and 21, inductances 20,22 and 23, and the capacities 14. ,If the signaling circuit side of the capacities 14 has a capacity to ground this must also be taken into account in designing.

Fig. 2 shows an arrangement for connecting the signaling circuit to the power line conductors 3. The arrangement of Fig. 2 corresponds to and replaces the capacities 14 in the circuit of Fig. 1. The aerials 63 are mounted upon suitable supports 64 and connected to the two conductors of the power line 3 which are to be used for transmission. When the power line 3 consists of three or more phases, any two conductors may be se- Hill lected as signaling conductors. The aerials 63 are at the potential of the power line conductors to which they are connected and must be insulated by suitable high voltage insulators 65. Adjacent to each antenna 63 is placed an aerial 66 which may be in a plurality of sections and preferably consists of, as illustrated in the present instance, two sections, one located upon each side of the antenna 63 and being equi-distantly placed therefrom. Each pair of aerials 66 is connected by a suit-able lead 67 to the signaling apparatus through the coupling circuit 13. The antenna or aerial arrangement thus described may be located either in a horizontal or a vertical plane. That is, the antenna 66 may be above and below the antenna 63 re spectively, or located to the sides thereof. This coupling arrangement has numerous advantages. A sufficiently large capacity between the power line and the signaling apparatus is readily attained. The supports 64; and the aerials 63 and 66-may be constructed in a manner to withstand extreme weather conditions and thus avoid danger of direct conductive contact between the signaling circuit and the power line even if that portion of the power line immediately adjacent the tit) antenna structure should break and fall to the ground.

Figs. 3, 4, 5 and 6 show modified forms of coupling circuits adapted to be used with aerial coupling capacities such as shown in Fig. 2. In each of these figures the capacities to ground of the aerials .63 are shown in dotted lines... This is' to emphasize the. fact that these capacities must always be taken into account in the ,design of the coupling circuit in order to give the coupling circuit any desired characteristics. In these figures, the fuses and vacuum gaps which may be used in practice have been omitted.

Tn Fig. 3. the coupling circuit comprises capacities 19 and 19 in series with the line and inductances 22 in shunt to the line. By proper designing such a circuit may be made to have a suitable transmission characteristic.

In Fig. t, the modification introduced consists of a capacity 68 in shunt to the line on the signaling circuit siderthus enabling a modified transmission characteristic to be obtained.

lln Fig. 5 separate leads are provided for connection to the high pass and low pass filters 11 and 12. Thus, the conductors 69 are connected to the high pass filter and the conductors 70 to the low pass filter. The inductances 7L have valuesdifterent from those of the inductances 72, thus providing for a transmission characteristic in the outgoing channel different from that in the incoming channel. The inductances 7 3 are preferably of similar values as are the capacitis 19. i 1

In Fig. 6, the modification introduced consists of the addition of the condenser 68 which, as in the case of Fig. 4, serves to enable the attainment of a different transmission characteristic for the coupling circuit.

Certain features of the system herein disclosed are described and claimed in the copending application of P. H. Evans, Serial N 0. 664,432. The claims in the present application are directed only to those features believed to be novel and which constitute the invention of applicant.

The invention claimed is:

1. In a two-way signaling system, terminal apparatus comprising incoming and outgoing channels, a selective circuit in each channel designed to pass waves of a certain frequency and to exclude waves of the frequency passed by the other, and means, operated as a result of an essential action in attempting to use said apparatus, for interchanging said selective circuits With respect to the incoming and outgoing channels.

2. In a signaling system, terminal apparatus comprising incoming and outgoing channels, a high pass filter normally con nccted to the outgoing channel and a low pass filter normally connected to the incoming channel, and means, actuated as a result of an ope *ator taking possession of said apparatus to call a distant station, to interchange said filters.

3. A system for duplex communication over a power line comprising a receiving circuit normally conditioned to receive calls of a predetermined wave frequency. a selective circuit normally conditioned to transmit incoming calling waves from said power line to said circuit, and means actuated by the first essential operation of calling another station to replace said selective circuit by another selective circuit designed to pass waves of a different frequency upon which the called station is designed to' reply.

4. In a system for duplex communication between two stations having similar transmission apparatus and similar reception apparatus, said transmission apparatus comprising an oscillator normally conditioned to generate oscillations of a certain predetermined frequency, and said reception apparatus being normally selective to oscillations of a diiferent predetermined frequency, means actuated by the removal of a receiver from its switchhook preliminary to calling a distant station to condition said oscillator for the generation of waves of said second named predetermined frequency, and to condition said receiving apparatus selective to said first named predetermined frequency and'means responsive to the arrival of calling waves to prevent the actuation of said first mentioned means by the removal of the telephone receiver from its switchhook in the act of answering.

5. In a duplex signaling circuit employing waves of two frequencies for each two-way communication, one wave being transmitted in each direction, incoming and outgoing channels, a selective circuit normally connected in each channel, said selective circuits being of different characteristics, and means operative for interchanging said circuits in order to transmit to the line groups of waves of one of said frequencies for calling a distant station.

6. In a signaling system comprising a plurality of stations, receiving apparatus at each station normally conditioned for the reception of incoming calls, a selective circuit for transmitting from the line to the receiving apparatus waves of a frequency used for calling in combination with means at one station for generating waves of the calling frequency and transferring said selective circuit from the receiving channel to the transmitting channel in order to transmit to the line waves of the calling frequency.

7. In a signaling system, a space discharge detector normally conditioned to .efliciently rectify groups of waves used for calling purposes, andmeans responsive to an operation necessary in using said system for talking to condition said detector, by changing the normal potential of its control electrode, for efficiently detecting voice modulated waves. 8. In a signaling system, a space discharge detector normally conditioned to efiiciently rectify groups of waves used for calling purposes and a relay operated by the removal of a telephone receiver from its switchhook for conditioning said detector, by changing the normal potential of its control electrode,

' to efficiently detect the voice modulated quencv waves, necte Waves.

9. In a party line system for communicating over a high voltage power line, a ringing system comprising a selector at each station responsive to a properly arranged group of impulses of alternating polarity, means at one or more stations for sending to the line groups of high frequency waves from which said impulses may be derived, a rectifying system at each station for producing unidirectional impulses from said high freand a relay operatively conbetween said rectifying system and said selector to convert said unidirectional impulses into impulses of alternating .polarity.

10. A circuit for connecting signaling apparatus at a station to a high voltage transmission line comprising a coupling circuit having the characteristic of a band pass filter with upper and lower'definite limits, capacities capable of withstanding the voltages of said transmission line adjacent to said line, the constants of said capacities entering into and determining in part the characteristic of said coupling circuit, two channels connected to the terminals of said band pass filter remote from the transmission line, a high pass and a low pass filter, respectively, included in said two channels, and means for automatically interchanging the high pass filter .and the low pass filter with respect to the two channels when the station operates as a calling station. I

11; A circuit for connecting signaling apparatus at a station to a high voltage transmission line comprising a band-pass filter-terminating at and being connected to said transmission line and including series condensers adapted to withstand the transmission'line voltage, two channels connected to the terminals of said filter remote from said transmission line, each of said channels comprising a filter adapted to exclude waves of certain range which the other filter is adapted to transmit, and means for automatically interchanging said channel filters with respect to the channels when the station operates as a calling station.

12. Ina signal receiving circuit, a plurality of space discharge repeaters arranged in tandem, a marginal relay connected to the output circuit of one of said repeaters and adapted to be actuated by a predetermined current fiowing thercthrough, an artificial line controlled by said relay whereby upon actuation of said relay, said artificial line is connected in tandem with said repeaters.

13. In a signaling system for duplex communication between stations having transmitting and receiving apparatus, means actuated by the removal of the receiver from the switchhookat a call originating station to energize oscillating, generating and amplifying waves within one frequency range to a distant station, means simultaneously actuated to render the call receiving apparatus at the call originating station responsive to waves within another frequency range which the called station is adapted to transmit in reply, incoming and outgoing channels containing selective elements and additional means controlled by the removal of the receiver from the switchhook at the transmitting station to interchange the selective elements normally connected to the incoming and outgoing channels at said station.

14. In a system for transmitting by means of high frequency waves, a circuit for rendering the high frequency transmission apparatus operative, means controlled by the removal of a receiver from its switchhook to establish said circuit, and means actuated as a result of etxending the communication channel to a low frequency line to maintain said first named circuit after the receiver has been restored to its switchhook.

15. In a system for signal transmission over high power lines, a signal station comprising apparatus controlled by the removal of the receiver from its switchhook for producing and transmitting to the line sufiicient.

power for transmission under normal conditions in comblnation with a relay controlled by the removal of the receiver from its switchhook and auxiliary amplifier apparatus controlled by said relay and normally conditioned for operative communication between said transmitting apparatus 1 and said line in order to transfer to the line sufiicient high frequency power for trans-v mitting under abnormal conditions.

In witness whereof, I hereunto subscribe my name this 21st day of September, D. 15 

